Left-digit Bias Research Articles

Left-digit bias in self-reported height

Left-digit bias is a cognitive bias wherein individuals assess the magnitude of numbers by emphasizing the leftmost digit. For instance, people often perceive the difference between $9.99 and $10.00 larger than that between $10.00 and $10.01, given the distinct left digits in the former two numbers. This study associates self-reported height with this cognitive bias. Taller stature is frequently associated with desirable attributes such as higher earnings and leadership positions; individuals may aspire to be taller and, consequently, report a height greater than their actual measurement. We posit that this inclination is more pronounced when combined with left-digit bias. In other words, individuals whose actual height ends in nine, such as 169 cm, are more likely to report their height as 170 cm than individuals with an actual height of 170 cm who report it as 171 cm. To conduct this analysis, we used data from an annual health survey of adolescents in grades 7–12. Our findings indicate that male adolescents exhibit a left-digit bias in reporting their height, whereas female adolescents do not. We contribute to the literature by providing new evidence of left-digit bias.

Focal points for giving

Leveraging the unique context of New York City taxi rides, we estimate that passengers are more likely to tip a suggested amount when presented with an integer tip suggestion, which also corresponds with an increase in average tip rates. We show that these results are not driven by rounding heuristics and are consistent with integers acting as focal points instead of left-digit bias. Focusing on a 2012 rate fare change that increased the probability of integer tip suggestions by 700%, our estimates imply a transfer from riders to drivers of approximately 250,000 dollars in 2013.

Left-digit bias in surgical decision-making for lumbar spinal stenosis

BACKGROUND CONTEXTLeft-digit bias is a behavioral heuristic or cognitive “shortcut” in which the leftmost digit of a number, such as patient age, disproportionately influences surgical decisions. PURPOSETo determine if left-digit bias in patient age influences the decision to perform arthrodesis with instrumentation vs decompression in lumbar spinal stenosis (LSS). DESIGNRetrospective cohort. PATIENT SAMPLEPatients with an ICD-10 diagnosis of lumbar stenosis or spondylolisthesis identified in the 2017-2021 National Surgical Quality Improvement Program (NSQIP) database. OUTCOME MEASURESThe primary outcome was the percent of patients who underwent arthrodesis with instrumentation (AwI). Matched age group comparisons without left-digit differences (ie, 76/77 vs 78/79, 80/81 vs 82/83, etc.) were performed to isolate the effect of the heuristic. Secondary outcomes including peri-operative events and complications were also compared within AwI and decompression cohorts. METHODSUsing CPT codes, procedures were classified as either AwI or decompression. Patients were grouped into 6 cohorts based on 2-year age windows (74/75, 76/77, 78/79, 80/81, 82/83, 84/85). The cohorts were propensity matched with neighboring age groups based on the presence of spondylolisthesis, demographics, and comorbidities. The primary comparison was between those aged 78/79 vs 80/81. RESULTSAfter matching, the primary cohort consisted of two groups of 1,550 patients (aged 78/79 and 80/81). Patients aged 80/81 were less likely to undergo AwI than patients aged 78/79 (23.5% vs 27.2%, p=.021). AwI procedures occurred at similar rates between age groups with the same left digit. Within the decompression and AwI cohorts, there were no differences in secondary outcomes between patients aged 78/79 and 80/81. CONCLUSIONSLSS patients aged 80/81 are less likely to undergo AwI than patients aged 78/79, regardless of comorbidities. This was not seen when comparing patients with similar left digits in age. Until objective measures of physiologic capacity are established, left-digit bias may influence clinical decisions.

Left-digit bias in out-hospital cardiac arrest: The JCS-ReSS study.

The left-digit bias (LDB), a numerical-related cognitive bias, not only potentially influences decision-making among the general public but also that of medical practitioners. Few studies have investigated its role in out-of-hospital cardiac arrest (OHCA). We retrospectively included all consecutive patients with OHCA witnessed by family members registered in the All-Japan Utstein Registry of the Fire and Disaster Management Agency between January 1, 2005, and December 31, 2020. Target outcomes were the percentage of bystander cardiopulmonary resuscitation (BCPR) performed by family members or paramedics and the percentage of prehospital physician-staffed advanced cardiac life support (ACLS). Using a nonparametric regression discontinuity methodology, we examined whether a significant change occurred in the percentages of BCPR and ACLS at the age thresholds of 60, 70, 80, and 90 years, which would indicate the presence of LDB. Of the 1,930,273 OHCA cases in the All-Japan Utstein Registry, 384,200 (19.9%) cases witnessed by family members were analyzed. The mean age was 75.8 years (±SD 13.7), with 38.0% (n = 146,137) female. We identified no discontinuities in the percentages of chest compressions, mouth-to-mouth ventilation, or automated external defibrillator (AED) usage by family members for the age thresholds of 60, 70, 80, and 90 years. Moreover, no discontinuities existed in the percentages of chest compressions, advanced airway management, and AED usage by paramedics or prehospital ACLS by physicians for any of the age thresholds. In conclusion, our study did not find any evidence that age-related LDB affects medical decision-making in patients with OHCA.

Does the left-digit bias affect prices in financial markets?

According to the left-digit bias, people pay more attention to the leftmost digits of a number and tend to disregard the last digits of that number. We investigate whether this bias affects traders' perception and pricing in a large financial market trading foreign exchange options. Our theoretical model predicts that the left-digit bias affects prices, causing a discontinuous jump in expected returns when comparing markets at threshold prices 10,20,…,90 with markets at prices just below these thresholds, such as 9.9,19.99, etc. The model predicts no discontinuity in returns among unbiased traders. Using a regression discontinuity approach over the returns of more than 1 million options, we find significant discontinuities in the expected returns, consistent with mispricing induced by the left-digit bias.

Effect of age-based left-digit bias on stroke diagnosis: Regression discontinuity design

BackgroundLittle is known about how left-digit bias— where humans tend to discretely categorize their decisions based on the left-most digit of the continuous variables—based on patients’ age affects the initial diagnosis of stroke patients. The aim of this study is to examine whether there is a discontinuous change in the ordering of imaging tests for stroke at the age threshold of 40 years old, which is indicative of left-digit bias, and whether the effect varies by patient sex. MethodsWe conducted a cohort study by regression discontinuity design (RDD). We analyzed the claims database from a nationwide working-age health insurance plan in Japan. Patients who had after-hours hospital visits from January 2014 through December 2019 were included in our analysis. The exposure is patients' age, and the primary outcome was physicians’ ordering imaging tests (CT or MRI) to diagnose stroke during the index visit. ResultsOf 293,390 total visits, 48,598 visits within data-driven optimal bandwidths of 6.0 years from the cut-off of 40 years were included for the RDD analysis (mean age 40.8 years [standard deviation 3.4], female 50.5%). The baseline probability of receiving imaging tests for stroke diagnosis was 0.9%. Physicians had a higher likelihood of ordering imaging tests when patients' age was above 40 years compared with when patients’ age was just below 40 years (adjusted difference, +0.51 percentage points [pp], 95%CI, +0.13 to +1.07 pp; P = 0.01). We found a significant discontinuous change in the ordering of imaging tests for stroke at 40 years for male patients (+0.84 pp, 95%CI, +0.24 to +1.69 pp; P = 0.009) but not for female patients. ConclusionsPhysicians have a cognitive bias in estimating stroke risk and, consistent with a left-digit bias, treat male patients aged 40 and just below differently. This pattern was observed only among male patients.

150. Left digit bias in deciding to fuse vs decompress in degenerative spondylolisthesis and stenosis: how age-related heuristics impact surgical decision-making

150. Left digit bias in deciding to fuse vs decompress in degenerative spondylolisthesis and stenosis: how age-related heuristics impact surgical decision-making

Unobserved heterogeneity and adjustment to behavioral bias: The case of used cars

With novel data on ex-post quality after used-car purchases, I evaluate left-digit bias, a type of inattention bias, for underlying quality of used cars. My main result is that the used-car market exhibits a quality discontinuity in parallel to a price discontinuity at 10,000 multiples of mileage. I discuss explanations for how quality adjusts to the price discontinuity. The explanations differentiate between exogenous and endogenous quality, and by the extent of the information asymmetry about quality. Quality assurance mechanisms, like used-car knowledge, trust, or recommendations, can reduce information asymmetry. Additional evidence on quality assurance shows that buyers use much more information — both before and after the purchase — than the pure inattention interpretation of left-digit-bias would suggest.

Heuristics in Self-Evaluation: Evidence from the Centralized College Admission System in China

Abstract Using administrative data on the Chinese National College Entrance Examination, we study how left-digit bias affects college applications. We find strong discontinuities in students' admission outcomes at 10-point thresholds. Students with scores just below multiples of 10 make more conservative college application choices that place them into less selective colleges and majors. In contrast, students who score at or just above multiples of 10 aim and achieve higher but are at greater risk of overshooting. The discontinuity reveals that, despite the educational and labor market consequences, students' self-evaluation based on exam scores is subject to information-processing heuristics.

Left-Digit Bias at Lyft

Abstract Left-digit bias (or 99-cent pricing) has been discussed extensively in economics, psychology, and marketing. Despite this, we show that the rideshare company, Lyft, was not using a 99-cent pricing strategy prior to our study. Based on observational data from over 600 million Lyft sessions followed by a field experiment conducted with 21 million Lyft passengers, we provide evidence of large discontinuities in demand at dollar values. Approximately half of the downward slope of the demand curve occurs discontinuously as the price of a ride drops below a dollar value (e.g. $14.00 to $13.99). If our short-run estimates persist in the longer run, we calculate that Lyft could increase its profits by roughly $160M per year by employing a left-digit bias pricing strategy. Our results showcase the robustness of an important behavioral bias for a large, modern company and its persistence in a highly competitive market.

More Than a Penny’s Worth: Left-Digit Bias and Firm Pricing

Abstract Firms arguably price at ninety-nine-ending prices because of left-digit bias—the tendency of consumers to perceive a $4.99 as much lower than a $5.00. Analysis of retail scanner data on 3500 products sold by twenty-five U.S. chains provides robust support for this explanation. I structurally estimate the magnitude of left-digit bias and find that consumers respond to a one-cent increase from a ninety-nine-ending price as if it were more than a twenty-cent increase. Next, I solve a portable model of optimal pricing given left-digit biased demand. I use this model and other pricing procedures to estimate the level of left-digit bias retailers perceive when making their pricing decisions. While all retailers respond to left-digit bias by using ninety-nine-ending prices, their behaviour is consistently at odds with the demand they face. Firms price as if the bias were much smaller than it is, and their pricing is more consistent with heuristics and rule-of-thumb than with optimization given the structure of demand. I calculate that retailers forgo 1–4% of potential gross profits due to this coarse response to left-digit bias.

The price paid: Heuristic thinking and biased reference points in the housing market

Does the power of reference points mean that minute differences in a purchase price then reverberate in future sales prices? In this research, I show that if previous sales prices are round numbers, defined as multiples of £1,000 (e.g. £231,000), subsequent sales prices entail a considerable premium relative to similar properties that were previously priced at charm numbers that are marginally below those round numbers (e.g. £230,999 or £230,950). Using a sample of repeat sales from the Greater London region from 1995 to 2017, I estimate the premium to be approximately 4 percent after controlling for property characteristics and a large set of fixed effects. Increasing public accessibility of information attenuates the effect. Tax considerations, financial constraints, and pricing errors cannot explain the result. I propose a framework of reference dependence and left-digit bias to explain the result, highlighting the presence of behavioural biases in household decisions, even when very high stakes are involved.

Assessing Heuristic Bias During Care for Patients Hospitalized for Heart Failure: Get With The Guidelines-Heart Failure.

Heuristic biases are increasingly recognized, and potentially modifiable, contributors to patient care and outcomes. Left digit bias is a cognitive bias where continuous variables are categorized by their left-most digit. The impact of this heuristic bias applied to patient age on quality of care in heart failure has not been explored. We examined participants admitted from 2005 to 2021 in the Get With The Guidelines-Heart Failure registry. To create 2 naturally randomized groups, isolating the effect of left digit bias, we dichotomized patients into those discharged within 60 days prior to their 80th birthday (N=4238) and those discharged within 60 days after their 80th birthday (N=4329). We performed multivariable logistic regression to assess the association between discharge date relative to 80th birthday and several in-hospital quality metrics and in-hospital outcomes. Among Medicare participants (N=2759), we performed adjusted Cox regression to analyze the relationship between discharge date and risk of 1-year mortality or readmission. Among 8567 patients, 50.4% were female, 73% were non-Hispanic White, and 42.9% had an ejection fraction ≤40%. Discharge date relative to 80th birthday was not associated with numerous in-hospital quality metrics or in-hospital outcomes on unadjusted or adjusted logistic regression. Among Medicare beneficiaries, there was no association between discharge date and risk of mortality or readmission at 1-year postdischarge (hazard ratio, 1.03 [95% CI, 0.95-1.12]; P=0.52). In a large registry of patients hospitalized for heart failure, we did not detect a left digit bias' with respect to age at discharge, which resulted in differential quality of care or outcomes.

Abstract 150: Left-digit Bias In Out-hospital Cardiac Arrest - JCS ReSS

Introduction: Left-digit bias, a cognitive bias, has been linked to medical errors in clinical decision-making. Although the impact of left-digit bias on outcome and behavior has previously been examined in the setting of in-hospital cardiac arrest, that in the setting of our-of-hospital cardiac arrest has not been fully evaluated. In the current study, we investigated the impact of left-digit bias on resuscitators’ behavior during out-of-hospital cardiac arrest (OHCA). Methods: The All-Japan Utstein Registry of the Fire and Disaster Management Agency is a nationwide, prospective, population-based OHCA registration system in the Utstein format. We retrospectively included all consecutive OHCA patients within three years below and above the age of 80 witnessed by family members from January 1, 2005, to December 31, 2020. The primary endpoints were the percentage of bystander-initiated cardiopulmonary resuscitation (BCPR) performed by family members or EMS and the percentage of prehospital physician-staffed advanced cardiac life support (ACLS). We compared the percentages of resuscitation performed by family members, emergency medical services (EMS), and physicians, by using a regression discontinuity methodology to evaluate if there was a dramatic change in the percentage of BCPR and ACLS performed rate at the age threshold of 80 years, which would imply left-digit bias. Results: Of total 1,930,273 cases of OHCA in the All-Japan Utstein registry, we enrolled total of 92,674 (4.8%) patients. The mean age of the population was 80.1 years; 61284 (66.1%) patients were men. There were 37,903 (40.9%) patients between the ages of 77 and 80, and 54,771 (59.1%) patients between the ages of 80 and 83. In this model, we identified no discontinuities in the level (risk difference, -0.50%; 95%CI -1.35% to 0.36%, 0.27%; 95%CI -0.29% to 0.84%, 0.68%; 95%CI -0.29% to 1.66%) for the percentage of BCPR by family members and EMS, and physicians’ ACLS, respectively. Conclusions: In conclusion, our findings did not imply that age-related cognitive bias affected the resuscitators’ behavior during out-of-hospital cardiac arrest.

79 is the new 70: Left digit bias in craniotomy

BackgroundLeft digit bias is the psychological phenomenon in which the difference between values is perceived as larger due to the value of the first digit. For example, an 80 year old may be perceived as much older than a 79 year old. We sought to determine if left digit bias is present in craniotomy for elderly patients with traumatic brain injury. MethodsPatients aged 69, 70, 79, and 80 with traumatic brain injury and an abbreviated injury scale severity of a minimum of 3 were included from the National Trauma Data Bank from the years 2012-2019. 38,908 patients were included. A Chi-squared Test was performed to compare the percentage of patients undergoing craniotomy. Results79 year olds had higher craniotomy rates than 80 year olds (7.8% vs 6.4%, P < 0.001). There was no difference in craniotomy rates between 69 and 70 year olds (8.2% vs 7.8%, P < 0.2622). ConclusionThis study suggests the presence of left digit bias in the decision to perform a craniotomy in patients aged 79 vs 80 with traumatic brain injury.

Modeling the left digit effect in adult number line estimation

Number line estimation tasks are frequently used to study numerical cognition skills. In a typical version, the bounded number line task, target numerals must be placed on a bounded line labeled only at its endpoints (e.g., with 0 and 100). Placements by adults, while highly accurate, reveal a cyclical pattern of over- and underestimation of target numerals. The pattern suggests use of proportion judgment strategies and is well-captured by cyclical power models. Another systematic number line bias that has recently been observed, but has not yet been considered in modeling efforts, is the left digit effect. Numerals with different leftmost digits (e.g., 39 and 41) are placed farther apart on a line than is warranted. In the current study (N = 60), adult estimates were obtained for all numerals on a 0–100 number line estimation task, and fit of the standard cyclical power model was compared with two modified versions of the model. One modified version included a parameter that underweights the rightward digit's place value (e.g., the ones digit here), and the other used the same parameter to underweight all digits' place values. We found that both modifications provided a considerably better fit for individual and median data than the standard model, and we discuss their relative merits and cognitive interpretations. The data and models suggest how a left digit bias might impact estimates across the number line.

Impact of Left-Digit Age Bias in the Treatment of Localized Prostate Cancer.

Left-digit bias is a phenomenon in which the leftmost digit of a number disproportionately influences decision making. We measured the effect of left-digit age bias on treatment recommendations for localized prostate cancer. We included men with clinically localized prostate adenocarcinoma in Surveillance, Epidemiology, and End Results from 2004 to 2018 and the National Cancer Database from 2004 to 2016. Primary outcomes were recommendations for radiation therapy and radical prostatectomy. Regression discontinuity was used to assess whether age increase from 69 to 70 years was associated with disproportionate changes in treatment recommendations. In Surveillance, Epidemiology, and End Results, discontinuities were found in the proportion of patients recommended for radiation among the entire cohort (effect size 2.2%, P < .01) and among patients with Gleason 6 (1.6%, P < .01), Gleason 7 (2.5%, P < .01), and Gleason ≥8 (2.1%, P < .01) cancer, while the proportion recommended for prostatectomy decreased in the entire cohort (-1.4%, P < .01) and in patients with Gleason 7 cancer (-2.4%, P < .01). In the National Cancer Database, discontinuity from age 69 to 70 was found in recommendations for radiation in the entire cohort (effect size: 3.1%, P < .01) and in patients with Gleason 6 (2.2%, P < .01), Gleason 7 (4.0%, P < .01), and Gleason ≥8 (2.3%, P < .02) cancer, while the proportion recommended for prostatectomy decreased at this cutoff in the entire cohort (effect size: -2.7%, P < .01) and patients with Gleason 6 (-2.2%, P < .01) and Gleason 7 (-3.7%, P < .01) cancer. In patients with localized prostate cancer, left-digit age change from 69 to 70 was associated with disproportionately increased recommendations for radiation and decreased recommendations for prostatectomy.

An assessment of left-digit bias in the treatment of older patients with potentially curable rectal cancer

BackgroundPatient age is associated with poorer rectal cancer treatment compliance. However, it is unknown whether left-digit bias (disproportionate influence of leftmost age digit) influences this association. MethodsThe patients diagnosed with stage I–III rectal cancer between 2006 to 2017 in the National Cancer Database were identified. The association between age and receipt of guideline-adherent care was assessed using mixed-effects multivariable analyses. ResultsAmong 97,960 patients, 46.2% received guideline-adherent overall treatment and 73.3% underwent guideline-adherent surgical resection. Of those who underwent guideline-adherent surgery, 86.4% received guideline-adherent radiotherapy and 56.6% received guideline-adherent chemotherapy. After risk-adjustment, each decade increase in age was associated with 36% decreased odds of guideline-adherent therapy (odds ratio = 0.64, 95% confidence interval = 0.63–0.65). Patients aged 58 to 59 (odds ratio = 1.15, 95% confidence interval = 1.02–1.27) and 78 to 79 (odds ratio = 1.28, 95% confidence interval = 1.08–1.51) had higher odds of guideline-adherent overall treatment compared with patients aged 60 and 80, respectively. However, there were no significant differences in the receipt of guideline-adherent treatment between patients aged 60 vs 61–62 and 80 vs 81–82. ConclusionOlder patients with rectal cancer are less likely to receive guideline-adherent care, and a left-digit bias is present. Geriatric assessment-guided treatment decisions could help mitigate this bias.

Heuristic thinking in the workplace: Evidence from primary care.

We study whether primary care physicians (PCPs) exercise left digit bias with respect to patients' age. Relying on a comprehensive administrative visit level data from a large Israeli HMO, we measure the intensity of patients' medical examination in visits that take place around a decadal birthday—a birthday that ends with zero—within a regression discontinuity framework. We find that in standard settings with clear patient information there is no evidence that PCPs exhibit left digit bias. However, when PCPs meet unfamiliar patients seeking immediate care, they are more likely to use basic diagnostic tests just above the decadal birthday threshold, indicating that under these circumstances, PCPs do use left digit bias.

Left digit bias in selection and acceptance of deceased donor organs

BackgroundOrgans suitable for donation are a scarce resource and maximizing the use of available organs is a priority. We aimed to determine whether there is a supply restricting left digit bias in organs offered and accepted for donors entering a new decade of age. MethodsPotential deceased organ donors (n = 105,387) who had any organs offered for transplantation from 2010 to 2019 Organ Procurement and Transplantation Network data were analyzed. Donors were identified 1 year before and after a decade altering birthday. ResultsAt age 70 there was a 5.4% decrease in the probability of any organ placement compared to 69 (95% CI 1.1–9.7). There was a decrease of 0.25 organs (95% CI 0.13–0.37) after age 70. ConclusionsThere was a significant left digit bias in the acceptance of any organs for transplantation at ages 60 and 70 as well as in the acceptance of a kidney at age 70.